A physical channel of a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) system adopts a four-layer structure including a super-frame, a radio frame, a sub-frame and a time slot/code. The length of a super-frame is 720 ms and is composed of 72 radio frames, and the length of each radio frame is 10 ms. In the TD-SCDMA system, each radio frame is divided into two sub-frames with the length of 5 ms. FIG. 1 is a structural diagram illustrating a time slot in a TD-SCDMA system according to the related art. As shown in FIG. 1, the time slot of each sub-frame is composed of seven main time slots with each length of 675 us and three special time slots. The three special time slots include a Downlink Pilot Time Slot (DwPTS, 75 us), an Uplink Pilot Time Slot (UpPTS, 125 us) and a Guard Period (GP, 75 us).
In the seven main time slots, a Ts0 is always allocated for a Downlink (DL), a Ts1 is always allocated for an Uplink (UL), and other time slots can serve as time slots for the uplink and can also serve as time slots for the downlink. The time slots of the uplink and the time slots of the downlink are separated by a transformation point. There are two transformation points (from the UL to the DL and from the DL to the UL) in each sub-frame with 5 ms in the TD-SCDMA system, and the positions of the transformation points depend on the configurations for UL and DL time slots of the cell.
A Cell Search (CSR) algorithm of the TD-SCDMA system is introduced below. FIG. 2 is a diagram illustrating functional modules in an initial CSR process in a TD-SCDMA system according to the related art. As shown in FIG. 2, the initial CSR process mainly includes four steps. At Step 1, a Synchronous Downlink (Sync-DL) code used by a current cell is searched out to complete DwPTS synchronization. At Step 2, a basic Midamble code and a scrambling code of the current cell are determined. At Step 3, multi-frame synchronization is achieved according to a phase modulation sequence of the DwPTS. At Step 4, information of a Broadcast Channel (BCH) is read.
Step 1 can include two sub-steps. At Sub-step 1, an approximate position of the DwPTS is found by using a correlation method or an energy window method. At Sub-step 2, the Sync-DL code is determined by using the correlation method. Sub-step 1 is used to accurately search for an initial position of the DwPTS, and thus, as a key step in the CSR, directly affects the subsequent CSR step.
A DwPTS position searching module is intended to find an approximate position of the Sync-DL code by using two methods. One is the energy window method for searching out according to the power distribution characteristics of the TD-SCDMA sub-frames, and the other is the correlation method for being correlated to 32 Sync-DL codes within the whole sub-frame range. Due to great computational work caused by the total correlation method, the energy window method is always adopted in an actual CSR process of the TD-SCDMA system.
The determination of the position of the DwPTS via the energy window method is introduced below. FIG. 3 is a diagram illustrating determination of a DwPTS position via an energy window method according to the related art. As shown in FIG. 3, in view of a structure of the TD-SCDMA frame, there is a GP of 32 chips on the left of the Sync-DL code, there is a GP of 96 chips on the right of the Sync-DL code, and the Sync-DL code itself has 64 chips. Due to low power of the GP, in terms of the time distribution for receiving power, compared with the GP, Sync-DL segment has relatively high power. A greater value is obtained by dividing the power sum of the Sync-DL segment by the power sum of 64 chips (32 chips at each side). The approximate position for the DwPTS can be determined by using the method. Thus, the approximate position for the DwPTS can be found by using a method for establishing a power feature window via a power shape of a receiving signal, wherein a calculation formula of an eigenvalue R is expressed as follows.
  R  =                    P        ⁢                                  ⁢        1                              P          ⁢                                          ⁢          2                +                  P          ⁢                                          ⁢          3                      .  
However, input data of actual Radio Frequency (RF) have multiple interference factors such as RF bottom noise and external electromagnet interference. The time selective fading of the channel, the offset of the sampling point or the like determines that the accumulated power for the DwPTS may greatly fluctuate in 64 chips. FIG. 4 is a diagram illustrating interference in the CSR according to the related art.
In view of the comprehensive influence from various intrinsic and extrinsic factors, an ideal eigenvalue calculation formula is only applicable to an ideal laboratory environment with relatively high Signal to Noise Ratio (SNR). Once the eigenvalue calculation formula is applied to a complicated field environment, the success rate for searching out the eigenvalue in the CSR will significantly decrease.
An effective solution is not proposed currently for solving the problem of relatively low success rate in a solution for determining a DwPTS position according to the related art.